1. Field of the Invention
The present invention relates to a printed circuit board for a high-speed semiconductor package and, more particularly, to a printed circuit board having a shield structure for high-speed signal transmission lines.
2. Description of the Related Art
The advance of data transmitting/receiving techniques may incorporate semiconductor products for transmitting high-speed signals, for example of several Gbps (Gigabits per second). Generally, high-speed semiconductor products may be manufactured in a ball grid array (BGA) package type. The BGA package type may require printed circuit boards (PCBs) having a signal transmission line structure. The PCB may provide a mechanical support to integrated circuit (IC) chips and electrical connection paths between IC chips and external devices.
FIG. 1 is a perspective view of a conventional PCB 10 for a high-speed semiconductor package.
Referring to FIG. 1, the PCB 10 may have a dielectric base layer 11, and signal transmission lines 12 formed on one surface of the dielectric base layer 11. Ground patterns 13 may be formed between the signal transmission lines 12 to reduce coupling noises, e.g., crosstalk, between the signal transmission lines 12.
A ground plane 14 may be formed on the other surface of the dielectric base layer 11. Vias 15 may penetrate through the dielectric base layer 11 and connect the ground patterns 13 to the ground plane 14.
The distribution density of the vias 15 may impact high frequency signal transmission characteristics, e.g., as by coupling caused by parallel plate waveguide mode propagation. The distribution density of the vias 15 may increase in proportion to signal transmission speed. The distribution density of the vias 15 may be limited by a number of factors, for example practical minimum diameter of the via 15, separation intervals between the vias 15, and distances between the vias 15 and adjacent ground patterns 13. In the case of through-hole vias, signal transmission line arrangements on the opposite surface may also serve as a limiting factor.
Further, the vias 15 may experience inevitable coupling. The signal transmission lines 12 may have open upper portions, and surface waves may be transmitted to the signal transmission lines 12 along the ground patterns 13. As a result, coupling noises may occur between the signal transmission lines 12.